The present invention relates to a variable displacement compressor that controls the inclination of a drive plate by adjusting the amount of refrigerant gas bled from a crank chamber. More particularly, the invention pertains to an outlet control valve used in such a compressor.
A typical variable displacement compressor has a drive shaft, which is rotatably supported in a crank chamber defined in the compressor housing. The housing includes a cylinder block. Cylinder bores are formed in the cylinder block. A piston is reciprocally housed in each cylinder bore. An inclined drive plate, or swash plate, is supported by the drive shaft in the crank chamber. The swash plate rotates integrally with and inclines with respect to the drive shaft. The swash plate converts rotation of the drive shaft into reciprocation of the pistons.
The inclination of the swash plate varies in accordance with the pressure in the crank chamber. The stroke of the pistons is changed according to the inclination angle of the swash plate, which varies the displacement of the compressor. To control the crank chamber pressure, either the flow rate of refrigerant gas delivered to the crank chamber or the flow rate of refrigerant gas released from the crank chamber must be controlled.
To control the amount of gas delivered to the crank chamber, an inlet control valve is located in a passage connecting the discharge chamber to the crank chamber. The crank chamber is connected to a suction chamber by a bleeding passage. A fixed restrictor is formed in the bleeding passage. The control valve adjusts the amount of refrigerant gas supplied to the crank chamber from the discharge chamber, thereby setting the crank chamber pressure to a desired level.
To control the amount of gas released from the crank chamber, an outlet control valve is located in a bleeding passage, which connects the crank chamber to the suction chamber. When a piston compresses refrigerant gas in the associated cylinder bore, refrigerant gas in the cylinder bore leaks into the crank chamber between the surface of the piston and the wall of the cylinder bore. The leaking gas is referred to as blowby gas. The blowby gas increases the pressure of the crank chamber. The outlet control valve adjusts the amount of refrigerant flowing from the crank chamber to the suction chamber thereby setting the crank chamber pressure to a desired pressure.
Using the outlet control valve, the crank chamber pressure is changed in accordance with the amount of refrigerant gas bled from the crank chamber. Therefore, to quickly change the crank chamber pressure, sufficient blowby gas must be constantly supplied to the crank chamber. However, blowby gas is a mere byproduct of gas compression by the piston. Thus, it is difficult to quickly change the crank chamber pressure using only blowby gas. Further, the amount of blowby gas is varied according to the rotation speed of the swash plate. Particularly when the swash plate speed is low, the amount of blowby gas is not sufficient. Therefore, the inclination of the swash plate, or the compressor displacement, cannot be changed quickly.
Providing a constant, adequate supply of blowby gas to the crank chamber is difficult. To avoid this problem, a supply passage may be provided to supply refrigerant gas from the discharge chamber to the crank chamber. However, the diameter of the supply passage needs to be extremely small (for example, 0.1 to 0.5 millimeters). Forming such narrow passages in compressor housings with a drilling machine shortens the life of the drilling machine. Compressor housings having such a supply passage are therefore not suitable for mass production.